It is often disadvantageous when an operator is unable to determine whether or not a photographic cassette has been loaded with a photosensitive sheet, without opening the cassette. To avoid this disadvantage, it has been proposed to include an indicator with the cassette which enables the operator to visually determine whether a sheet of film is present or absent within the cassette.
U.S. Pat. No. 4,394,772 discloses a pair of spaced plates, one of which is provided with a solar battery connected to a liquid crystal indicator. When the cassette is empty of film, the plates are in contact with one another, causing shorting and resulting in a blank indicator face. When the cassette is loaded with a film, the short-circuiting plates are isolated from each other by the film positioned therebetween, resulting in the indicator face displaying the word "FILM". In low light levels, as might be found in a photographic dark room used to load or unload film, such a solar apparatus may not provide a display indicating that the film is loaded.
U.S. Pat. No. 4,248,172 discloses an indicating element whose inner end is received in a recess of a cassette when film is absent from the cassette. The presence of the film into the cassette prevents the indicating element from entering the recess. The position of the indicating element may be ascertained either by touch or observation. With such an arrangement, visual verification may not be readily apparent.
U.S. Pat. No. 4,807,271, commonly assigned, discloses an end-loading cassette wherein a film sheet moving along an inlet path to its loaded position within the cassette causes its leading edge of the film sheet to slideably engage an indicator member, and move the indicator between a first and second position.
While the above apparatus have achieved a certain degree of success, a need continues to exist for a film presence indicator for use with a hinged cassette which provides an external visual verification which is readily apparent and easily readable by an operator, even in safe-light illuminated dark rooms. That is, such a film presence indicator should provide a large visual effect from a small travel distance of an actuating means. Further, such an apparatus must be compact since space is limited, long lasting, manufacturable, and if the film is photosensitive, ensure that the cassette remains light-tight.